This film predates Amsterdammned as a film with a scuba suit wearing psycho killer. Problem with scuba suits is that you can't move around well on land in them. That is no problem for this killer since many of his victims seem to literally walk right into his arms.
The series of killings, part of this film is the weak section, but the lair of the killer (which I won't spoil by telling what it is) final reel is worth the wait. Everything improves including the music during the final reel and when it's all over you'll feel better about the whole film than you will during parts in the middle. Most of the best images in the film are from that final 10 minutes but there are definitely some you'll remember.
Comedy intentional and unintentional also helps keep the film going. At least the American print I saw has almost no on screen violence, other than the macabre chase at the end. Dubbing is pretty poor but that goes with the territory.
A restoration of the original Italian version would be a great improvement I'm sure. Fans of films set in Venice will want to give this a look. Too bad the budget couldn't allow for any underwater photography that would have helped the early sections a great deal. All I'll say about the killer's identity is that in some Giallos the revelation is one of those, who was that guy again? In some Giallos that's the way it is.